238 Correspondence — Rev. 0. Fisher. 



exhibited and described before the Society November 17, 1903, and 

 subsequently named rathite a, but of which no complete description 

 has yet been published. — R. H. Solly: Two new minerals from the 

 Binnenthal, Switzerland. Both are probably sulpharsenites of lead, 

 being lead-grej r in colour and giving a chocolate-coloured streak ; one, 

 which is rhombohedral-diplohedral, and has an angle 1 1 1 : 1 00 = 38° 1 8', 

 is probably isomorphous with trechmanite, while the other may be 

 orthorhombic, the angle 100 : 110 being 58° 18', but no measurable 

 end faces were observed. — J. B. Scrivenor: Notes on Cassiterite in 

 the Malay Peninsula. Cassiterite from a mine at Gopeng contains 

 ilmenite and magnetite, and is attracted by the magnet ; it also 

 occurs mixed with tourmaline pseudomorphic after an hexagonal 

 mineral, probably quartz. Arthur Russell : Notes on the occurrence 

 of Dundasite in Derbyshire and Co. Galway, and of Bertrandite in 

 Cornwall. Dundasite was discovered at Mill Close Mine, Wensley, 

 Derbyshire, as snow-white spheres associated with greenockite, fluor, 

 cerussite, calamine, etc., and at Clements lead mine, Carrowgarriff, 

 near Maam, co. Gralway, associated with allophane and cerussite, 

 and bertrandite was found in platy crystals on old specimens of blende 

 from Wheal Yor, Breage, Cornwall, and as trillings, measuring up 

 to 4 mm. in length, on a specimen from Wheal Metal, Breage, 

 Cornwall, which had been presented as albite to the British Museum 

 in 1870; in the latter case the crystals were similar to those from 

 Pisek, Bohemia, described by C. Vrba. — Dr. J. Drugman : On Quartz- 

 twinning. The possible varieties of twinning of quartz were discussed, 

 with special reference to the rhombohedron type, a specimen of which 

 was exhibited. — T. V. Barker: Crystallographic Notes. Two new 

 forms found on crystals of inosite confirm the hypohexagonal type 

 of symmetry suggested by Fedorow. The rhombohedral modification 

 of potassium nitrate, unlike sodium nitrate, does not arrange itself 

 regularly when deposited on a cleavage piece of calcite ; the crystals 

 are very unstable, and rapidly pass into the ordinary orthorhombic 

 form. A parallel growth of calcium chromate on the isomorphous 

 mineral gypsum was obtained. New forms have been observed on urea 

 nitrate which enabled the axial ratio b : c for the first time to be 

 calculated; the crystals have large birefringence, and, when grown in 

 ■a drop, are nearly always twinned. 



COREESPONDEITCE. 



THE LAND-ICE HYPOTHESIS. 

 Sir, — In his letter in the last number of the Magazine (for April, 

 p. 189), Mr. Deeley suggests that ice resting on frozen ground " would 

 freeze to it and drag it along ". I remember to have seen evidence 

 of the rock on which Boulder-clay rests having been thus dragged along. 

 The hill between Hastingfield and Barrington, near Cambridge, consists 

 of Lower Chalk, or clunch, capped by Boulder-clay. Near the south 

 crest of the hill, on the west side of the road, there is a large clunch 

 pit, now little used, and when I last saw it the section was concealed. 

 But a good many years ago the junction of the Boulder-clay and the 



